Problem: $J$ $K$ $L$ If: $ JK = 9x + 3$, $ KL = 2x + 9$, and $ JL = 78$, Find $KL$.
Explanation: From the diagram, we can see that the total length of ${JL}$ is the sum of ${JK}$ and ${KL}$ $ {JK} + {KL} = {JL}$ Substitute in the expressions that were given for each length: $ {9x + 3} + {2x + 9} = {78}$ Combine like terms: $ 11x + 12 = {78}$ Subtract $12$ from both sides: $ 11x = 66$ Divide both sides by $11$ to find $x$ $ x = 6$ Substitute $6$ for $x$ in the expression that was given for $KL$ $ KL = 2({6}) + 9$ Simplify: $ {KL = 12 + 9}$ Simplify to find ${KL}$ : $ {KL = 21}$